To the editor, RE: No entry for immigrants with HIV (Toronto Star 21/09/00) The decision by Citizenship and Immigration Minister Elinor Caplan to test all immigrants for HIV is not only ethically questionable but also scientifically unsound. Rather than being "in the public-health interests of Canadians", it is sure to have a devastating effect on thousands of people's lives. The law of positive predictive value is a simple statistical fact that has profound implications for people subjected to HIV testing. Any test, regardless of its accuracy, performs badly in a population where very few people are expected to be infected. This applies to immigrants and pregnant women, two groups now subject to mandatory or routine HIV testing in Canada. Ron St. John of the federal Laboratory Centre for Disease Control claims "It is not known how many HIV-infected immigrants enter Canada but the estimate is one in 1,000." If a test is 99% accurate (which is optimistic), in a population where one in 1,000 are predicted to be infected there should be 99 true positives for every 999 false positives if 100,000 people are tested. That gives us a positive predictive value of 10%. Are we willing to condemn nine people to a false HIV positive diagnosis for every one actually HIV positive person we screen out? What would be the cost-benefit analysis of running 100,000 HIV tests to screen out 99 infected people? Some organizations like the American Foundation for AIDS Research (AmFAR) would like us to believe that HIV tests are 99.9% accurate. Even when this wishful figure is applied to the immigrant scenario we are left with a 50% chance of a false positive result. A review of the scientific literature on the practicality of HIV screening shows that most scientists seldom claim more that 99% or 99.5% accuracy. Repeat testing might clear up a false positive in some cases, such as laboratory error or sample mix up, but certain immunological conditions can cause a patient to test false positive repeatedly due to cross-reactions. Dr. Philip Berger points out that "Since HIV prevalence is higher in African countries, this would be a good way of keeping out immigrants from those areas." Also of higher prevalence in African countries are diseases and conditions that can leave people susceptible to a false positive HIV test result such as: tuberculosis, malaria, leprosy, hepatitis, recent viral infection, prior pregnancy, hypergammaglobulinemia (high levels of antibodies), alcoholic liver disease, "sticky" blood (in Africans), anti-collagen antibodies (found in gay men, Africans of both sexes, and haemophiliacs), etc. It may be impossible to sort out this problem of cross-reactions and the South African government has just asked an international panel of experts to try to resolve this very problem. To label prospective immigrants HIV positive and then send them back to countries where there may be grave social stigma about HIV and little or no health care or support services could amount to a death sentence. Everyone including immigrants, at the very least, should be assessed as to the appropriateness of HIV testing on a case by case basis assessing the person's relative risk of HIV infection and clinical history. Everyone has a right to proper counseling, disclosure of the risk of false positive results and the freedom to make an informed choice about HIV testing. Robert Johnston Robert Johnston is co-founder of HEAL Toronto (http://healtoronto.com) and first author of the Durban Declaration Rebuttal (http://thedurbandeclaration.org). For further explanation: HIGH RISK OF FALSE-POSITIVE HIV TESTS http://healtoronto.com/pospre.html THE PERFORMANCE RATE FOR THE COMBINED ELISA AND WESTERN BLOT HIV TEST - IS 99% ACCURACY GOOD ENOUGH? THE ANSWER: NO! http://healtoronto.com/stine_hivtests.html THE IMPORTANCE OF DISEASE PREVALENCE IN HIV TESTING http://healtoronto.com/amfar_hivtest.html SCREENING FOR HIV: CAN WE AFFORD THE FALSE POSITIVE RATE? http://healtoronto.com/testing_meyer.html FACTORS KNOWN TO CAUSE FALSE POSITIVE HIV ANTIBODY TEST RESULTS with a complete list with references: heal/testcross.html  TORONTO
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